A recent article from the Hindu ( a well-read English daily in India) discusses if the erratic behaviour of this year’s monsoon is due to “man-made” factors (increased CO2, aerosols etc) and whether such factors may adversely impact monsoon behaviour in future. This year’s monsoon has been erratic in its progress since early june, but this is not unusual! Rarely ever, monsoon season progresses ‘smoothly’ with evenly distributed rainfall everywhere! This year’s monsoon was projected by most climate models to be a deficient monsoon and it now appears that this year’s monsoon will go down as another deficit monsoon like in 2009, 2004 and 2002.

However, this year’s monsoon has also produced some heavy rainfalls and extensive flooding! Early in June there was extensive flooding in the northeast, then in southeast and since the last three weeks, there have been heavy rains and localized flooding in parts of central India! In some locales rainfall amounts of 100mm or more per day have occurred in parts of central India. Also western and northwestern parts of India have received some decent rains in last ten days or so. The monsoon report from the India Met Department for the week 8-15 August 2012 shows cumulative rainfall since June.

Yes, it is true that overall the large-scale monsoon circulation patterns have weakened in the last fifty years, contrary to most climate models’ projection of a ‘more vigorous’ monsoon in a warming world! Why has the large-scale monsoon weakened in the last fifty years is a ‘mystery’ and there is a definite need to investigate this aspect further. Are aerosols ( identified as ABC-Asian Brown Cloud) impacting monsoon adversely? Indian monsoon circulation patterns are primarily governed by large-scale atmosphere-ocean patterns ( the ENSO phase, the IOD-Indian Ocean Dipole in the equatorial Indian Ocean, the equatorial stratospheric QBO- Quasi-Biennial Oscillation, the Eurasian winter snow accumulation, etc) and are NOT impacted by aerosols or the recent warming of the earth’s climate at this point in time.

Seasonal prediction of monsoon is still fraught with several uncertainties and most climate models have achieved only a limited success in simulating or predicting monsoon rainfall on a seasonal time-scale. A simple operational model (see my ppt talk at Heartland Institute’s Conference in May 2012) can often provide a useful guidance for seasonal prediction of monsoon rainfall over India and vicinity.